Over the past fifteen years, personal computers have enjoyed a progressively increasing popularity, including portable computers of the type commonly known as “laptop” and “notebook” computers. During this same time period, significant advances have been made in the design of the processors used in personal computers, including portable computers. In this regard, the amount of circuitry which can be fabricated in a given area of an integrated circuit has increased significantly, thereby facilitating the implementation and fabrication of significantly more sophisticated processor designs. Further, the operational capabilities of processors have increased dramatically, and there have also been significant increases in the speed at which processors can operate.
A side effect of these technological advances is that state-of-the-art processors and other integrated circuits used in personal computers produce significantly more heat during normal operation than their predecessors did only a few years ago. In some systems, the processors and related components are operated at clock speeds significantly below their maximum rated clock speeds, in order to reduce the amount of heat generated, and thus avoid the need to provide active cooling. However, operating the processor at a speed less than its maximum rated speed decreases the capability of the system, and thus the value of the system in the eyes of consumers, which is undesirable. Therefore, and focusing specifically on processor chips, technology has reached a point where, in order to operate a processor at its maximum rated speed while effectively dissipating the heat which is generated, it is relatively standard for a desktop computer to have a forced-air cooling arrangement for the high-performance processor used in it. In particular, it is common to dedicate a relatively large heat sink and/or a powerful fan to the specific task of cooling the processor of a desktop computer. However, while these cooling arrangements have been generally satisfactory for use in desktop computers, they are not entirely satisfactory for use in portable computers.
More specifically, due in part to marketing efforts and consumer preferences, portable computers have evolved in design to a point where they are relatively thin and lightweight. In order to accommodate in a portable computer the type of cooling arrangement that has now become common in desktop computers, there would have to be an increase in both the thickness and weight of the portable computer. But an increase in the weight and/or thickness of a portable computer is undesirable from a commercial perspective, because it runs contrary to consumer preference for thin and lightweight units. Another significant marketing criteria for portable computers is the length of time that a fully-charged battery can run a portable computer before the battery becomes discharged. The powerful fans used in many desktop cooling arrangements would tend to consume a significant amount of battery power if used in a portable computer, and would thus undesirably shorten the effective battery life. Although a larger battery could be used, this would result in an increase in the size and/or weight of the portable computer, which as discussed above is undesirable.
The above-mentioned cooling arrangements for processors provide little or no benefit in regard to cooling of other circuit components that are separate from but associated with the processors. To date, it has typically not been necessary to provide components other than the processor with a direct cooling arrangement. However, advances in technology have increased the amount of heat generated by these other types of components, to the point where more effective cooling techniques are needed for these components.
Some prior attempts have been made to provide effective cooling in portable computers, but the results have not been entirely satisfactory. For example, heat pipes have been used to conduct heat from an interior component to an external finned heat sink, but the heat sink adds undesirable weight. Although the additional weight can be reduced to some extent by making the heat sink from a lightweight material such as magnesium, magnesium is relatively expensive, and the added expense is undesirable. As another example, some portable computers have vents provided in upper and/or lower portions of the housing, in order to facilitate cooling through natural convection currents. However, this approach provides only limited benefit, and technology is reaching a point where this type of natural convection cooling is simply inadequate to remove the amount of heat that is being generated.